This invention relates to novel metal coatings which exhibit exceptional resistance to corrosion and wear. More particularly this invention relates to metal coatings containing nickel, cobalt, boron and thallium and to the reductive deposition of said coatings on the surfaces of substrate articles from aqueous solutions at high pH.
The plating or deposition of metal alloys by chemical or electrochemical reduction of metal ions on the surface of an article to modify its surface characteristics for both decorative and functional purposes is well known in the art. Of particular commercial significance is the deposition of metal/metal alloy coatings on both metal and activated non-metal substrates to enhance surface hardness and resistance to corrosion and wear. Nickel-boron and cobalt-boron alloy coatings are recognized in the art for their hardness and associated wear-resistance. The patent literature reflects an ongoing research and development effort in the area of nickel-boron/cobalt-boron coatings with the goal of producing still harder, more corrosion resistance coatings. See, for example, U.S. Pat. Nos. 3,738,849; 3,045,334; 3,674,447; and 2,726,710. Bellis U.S. Pat. No. 3,674,447 describes nickel-boron and cobalt-boron coatings of improved hardness containing controlled amounts of thallium dispersed throughout the coatings. It has now been discovered that coatings containing both nickel and cobalt in combination with boron and thallium exhibit marked advantages over the thallium-containing nickel/boron or cobalt/boron coatings described by Bellis. Metal alloy coatings in accordance with the present invention containing boron, thallium and nickel and cobalt are more wear resistant and remarkably more corrosion resistant than those described in the prior art.
Electroless coatings containing both nickel and cobalt are described in U.S. Pat. Nos. 3,378,400 and 3,432,338. However in each of those patents a hypophosphite, and not a boron-containing reducing agent was used to deposit said coatings. Similarly U.S. Pat. No. 3,562,000 exemplifies deposition of a metal coating from a bath containing both cobalt chloride and nickel chloride using sodium hypophosphite. Although it is disclosed in that patent that other suitable reducing agents, including borohydrides, could be used in the numbered examples in place of the preferred hypophosphite, there is provided no description of the improved coatings in accordance with this invention.
It is therefore a general object of this invention is to provide improved metal coatings containing both nickel and cobalt, boron and thallium.
A further object of this invention is to provide an article of manufacture coated on at least a portion of its surface with a hard, ductile, wear and corrosion resistant metal coating comprising nickel an cobalt, boron and thallium.
Still a further object of this invention is to provide a heterogeneous electroless metal alloy coating containing both nickel and cobalt, boron and thallium having a metal concentration gradient in thickness cross-section.
Another object of this invention is to provide an electroless metal alloy coating presenting a corrosion and wear resistant surface comprising amorphous nodular deposits of nickel, cobalt, boron and thallium.
Yet another object of this invention is to provide coating baths from which a hard, ductile, wear and corrosion resistant coating can be deposited on at least a portion of the surface of a metal or activated non-metal substrate.
Those and other objects of this invention will be apparent to those skilled in the art from the following summary and detailed description of the invention.